1. Field of Invention
The present invention relates to loudspeaker apparatus and particularly to a loudspeaker that has an enhanced chamber located in front of a speaker unit.
2. Related Art
“Audio” literally means, “I hear” in Latin. The human ear can hear a frequency range between 16 and 1600 Hz. In a broad definition, any things that can generate sound may be called an audio source. For instance, a compact disk (CD), langspielplatte (LP), recording tape, FM/AM broadcasting, a microphone and the like are audio sources. Some audio sources cannot generate sound audible to human beings, so an electronic device has to be used to generate and transmit electronic signals, and a speaker has to be used to broadcast the sound audible to human ears. In one aspect, any device that can generate sound and receive electronic signals can be called a speaker.
The acoustic wave is a vibration generated by a solid, liquid or gas medium under pressure. The acoustic wave generated by the speaker is formed by vibration of a diaphragm after having received electronic signals that cause alteration of air pressure in the surrounding environment, and then the acoustic wave is received by human ears to become audible sound.
There are many types of speakers on the market. FIG. 1 illustrates a conventional speaker 10, which includes a closed cabinet 100, a diaphragm 110, a damper 120, a magnetic member 130, a voice coil 140 and a frame 150. The diaphragm 110, damper 120, magnetic member 130 and voice coil 140 are mounted onto the frame 150 to form a speaker unit that can generate sound. Then the speaker unit is installed on the closed cabinet 100.
The voice coil 140 is located on one end of the diaphragm 110 corresponding to the magnetic member 130, and located in the magnetic field generated by the magnetic member 130. When the electric signal passes through the voice coil 140, a magnetic force alteration occurs that interacts with the magnetic field of the magnetic member 130. The voice coil 140 alters according to the electronic signal. And the magnetic member 130 is attracted or repulsed to drive the diaphragm 110 outwards or inwards and lead to a conical portion of the diaphragm 110 moving like a piston for generating acoustic waves by compressing or releasing air. The cabinet 100 at the rear end of the speaker unit aims to prevent offsetting of the air pressure alterations in front of the diaphragm 110 and on the rear side of the diaphragm 110. The material, closed effect and mounting location of the cabinet 100 determine the acoustic characteristics generated by the speaker unit.
Production techniques of the speaker are known in the art. For instance, U.S. Pat. No. 6,817,084 discloses a fabrication technique for speakers that include a magnetic circuit disposed in a center hole of a bracket with a voice coil, a voice coil bobbin, a frame and a pole yoke mounting thereon to improve the acoustic quality of the speaker.
The interior space of a vehicle for installing the speaker is limited and the seating positions of listeners may be not symmetrical, so it is more difficult for the speaker to generate desired acoustic characteristics, tone and sound volume on a vehicle than a normal environment. In addition, the decorations of vehicle, which may have acoustic absorption and acoustic reflex effects, may cause phenomena such as resonance, stationary wave, time lag, phase deviation, phase difference, and the like. Hence installing the speaker on the vehicle is a great challenge. U.S. Pat. No. 6,819,767 discloses a sound reproduction apparatus for vehicles. It has a left-channel voice coil and a right-channel voice coil coupled co-axially on a voice coil bobbin. U.S. Pat. No. 6,843,345 also discloses a speaker for vehicles that is easily to be installed on the car door. Also, the platform space from the rear seat to rear glass can be used as a resonant chamber for the speaker installed on the platform behind the rear seat. As the conventional speaker generally is quite bulky, in recent years a panel speaker has been developed. U.S. Pat. No. 5,701,359 discloses a related technique. In the technique, a voice coil is attached to the bottom side of a diaphragm, and then installs adequate dampers and magnetic members to drive the diaphragm to generate acoustic waves. The panel speaker is much thinner than the conventional speaker, but its medium and bass sound effect is not as rich and desirable as the conventional speaker. Its output power also is lower than that of the conventional speaker. Moreover, the panel speaker has a narrower sound spectrum than the conventional speaker due the limitation of its structure. As the technique of the conventional speaker is well developed, it is still the mainstream of the market, and is not yet widely replaced by the new panel speaker.
The diaphragm is the key element of sound effect in the speaker. It may be made from a wide variety of materials, but paper is mostly used as main material. However, after World War II, polymer film has been gradually adopted for making diaphragms. Recently, a vacuum plating technique has been developed that can deposit a thin layer of metal carbon on the diaphragm by vaporization. Besides, making a large and thin diaphragm is quite difficult because the effects of material properties, thickness, type and thickness of the plating film, and supporting method will affect its quality somehow. Also, during the production, time, temperature and humidity are factors to be considered. Related fabrication techniques can be found in U.S. Pat. Nos. 5,206,466, 4,772,513 and 5,701,359.
In addition, installing the speaker on small electronic devices such as mobile phones, personal digital assistants (PDAs), or notebook computers also is a big concern. U.S. Pat. No. 6,834,744 discloses a related technique. The objects of the patent are to reduce the positive phase and negative phase phenomena, to reduce the size of speaker, and to obtain louder volume. It mainly installs a speaker unit in a mobile phone. Also, the mobile phone has a front acoustic aperture on the backside to emit sound from the front side of the speaker unit. The speaker unit further has a rear acoustic aperture on the rear side, so sound can be emitted from a memory card slot on one side of the mobile phone. Thus it provides two acoustic wave-traveling channels.
The aforesaid conventional techniques propose many techniques to improve the sound effect of the speaker, that take into account physical characteristics, a device structure, material, internal element configuration and the like. However, most conventional speakers have to rely on a cabinet located on the rear side of the speaker unit. Otherwise, the sound effect is not rich enough and the sound volume is smaller.
In terms of handheld data processing devices such as mobile phone and PDA, they already have other electronic elements located therein. There is little room available for installing the speaker, so the sound effect and volume is also limited. If the sound volume is driven to the maximum level, the air at the front side of the speaker unit will be offset with each other and broken sound is generated.
Moreover, the conventional handheld data processing devices generally have a small rear cabinet attached to the case. The case has a corresponding sound emission aperture on the front side to emit sound, but external articles such as dusts easily enter the case through the aperture and result in degrading of the sound effect of the speaker. The electronic elements located inside also are affected.